Physics Electricity and Magnetism 5 — Questions and Answers
Question 1: A solenoid has 1,000 turns, a length of 0.5 m, and a cross-sectional area of 0.01 m². What is its inductance? (μ₀ = 4π×10⁻⁷ H/m)
- 25.1 μH
- 2.51 mH
- 25.1 mH (Correct answer)
- 251 mH
Correct answer: 25.1 mH
L = μ₀N²A/l = 4π×10⁻⁷ × 10⁶ × 0.01 / 0.5 ≈ 25.1 mH.
Question 2: What is the equivalent capacitance of two capacitors, 4 μF and 12 μF, connected in series?
- 16 μF
- 48 μF
- 3 μF (Correct answer)
- 8 μF
Correct answer: 3 μF
1/C_eq = 1/4 + 1/12 = 3/12 + 1/12 = 4/12, so C_eq = 3 μF.
Question 3: When a conductor is placed in electrostatic equilibrium inside an external electric field, the electric field inside the conductor is:
- Equal to the external field
- Twice the external field
- Zero (Correct answer)
- Perpendicular to the external field
Correct answer: Zero
Free charges redistribute until the internal field is canceled, resulting in zero net field inside the conductor.
Question 4: The power dissipated in a resistor R carrying current I is expressed as:
- P = IR
- P = I²R (Correct answer)
- P = V/R
- P = IR²
Correct answer: P = I²R
Power dissipated as heat in a resistor is P = I²R, derived from P = IV and V = IR.
Question 5: Two long parallel wires carry currents in the same direction. They will:
- Repel each other
- Attract each other (Correct answer)
- Experience no force
- Spin around each other
Correct answer: Attract each other
Parallel currents in the same direction create magnetic fields that pull the wires toward each other.
Question 6: What is the SI unit of magnetic flux?
- Tesla
- Weber (Correct answer)
- Henry
- Gauss
Correct answer: Weber
Magnetic flux is measured in Webers (Wb), where 1 Wb = 1 T·m².
Question 7: In Kirchhoff's Voltage Law (KVL), the sum of all voltage drops around any closed loop in a circuit equals:
- The total current in the loop
- The supply voltage only
- Zero (Correct answer)
- The equivalent resistance
Correct answer: Zero
KVL states that the algebraic sum of all voltages around any closed loop is zero (energy conservation).
Physics Electricity and Magnetism 5
A solenoid has 1,000 turns, a length of 0.5 m, and a cross-sectional area of 0.01 m².
What is its inductance? (μ₀ = 4π×10⁻⁷ H/m)